The present invention relates to mark verification systems and more specifically to a method for calibrating a mark verification system wherein a verifier reader commences calibration when information in an image obtained by the verifier indicates that a calibration process should commence.
Many different industries require that marks be applied to manufactured components so that the components can be tracked during distribution, when installed or assembled, during maintenance processes, during use and after use. For instance, in the jet engine industry, jet engines include, among other components, turbines that include turbine blades that are manufactured in various size lots. Here, each turbine blade is marked when manufactured so that the blade can be tracked. Prior to the blade being disposed of, if any defect is ever detected in the blade, the defect can be traced back to a lot and a manufacturing process associated therewith so that any possible defects in other blades of the lot can be identified. Where marks are applied directly to components/parts, the marks are generally referred to as direct part marks (DPMs).
To directly mark components, known marking systems have been set up that include a marking station that applies a mark to a component. For instance, in at least some cases a marking station will apply a DataMatrix barcode symbol to each manufactured component where a DataMatrix symbol is a two-dimensional barcode that stores from 1 to about 2,000 characters. An exemplary DataMatrix symbol is typically square and can range from 0.001 inch per side up to 14 inches per side. As an example of density, 500 numeric only characters can be encoded in a 1-inch square DataMatrix symbol using a 24-pin dot matrix marking machine.
Despite attempts to apply marks that can be read consistently thereafter, sometimes mark application errors occur such that the mark cannot be subsequently consistently read and decoded properly. For instance, in some cases the surface to which the mark is applied may be somewhat discolored so that the contrast of the mark to the background of the application surface is not optimal. As another instance, in some cases where a mark consists of a plurality of dots, the dot sizes may be too large so that spaces there between are not perfectly discernible or the dot sizes may be too small to be recognized by some types of readers. As still other instances, axial non-uniformity of grid non-uniformity of the applied mark may be too great to reliably read. Many other mark metrics may be imperfect and may render mark difficult if not impossible to decode using many readers.
Whether or not a mark that has been applied to a component is readable often depends on the reading and decoding capabilities of a reader used to read and decode the mark. For instance, some relatively complex and expensive readers are capable of reading extremely distorted marks while cannot read marks that are not almost perfect.
To verify that applied marks are of sufficient quality to be read by readers at a specific facility (i.e., by the least sophisticated reader that is used at a specific facility), often marking systems will include, in addition to a marking station, a stationary verification station and at least a portion of a transfer line to transfer freshly marked components from the marking station to the verification station. Here, after a mark is applied to a component, the component is transferred via the transfer line to the verification station where the mark is precisely aligned with an ideal stationary light source and a stationary camera/mark reader that is juxtaposed such that a camera field of view is precisely aligned with the mark. After alignment, the reader reads the mark and attempts to verify code quality.
Verification can include several steps including decoding the mark and comparing the decoded information to known correct information associated with the mark that should have been applied. In addition, verification may also include detecting mark size, geometric mark characteristics (e.g., squareness of the mark), symbol contrast, quantity of applied ink, axial non-uniformity, grid non-uniformity, extreme reflectance, dot diameter, dot ovality, dot position, background uniformity, etc.
When a mark does not pass a verification process (i.e., mark quality is low), the marked component may be scrapped to ensure that the marked component does not enter distribution channels.
When a marked component passes a verification test at a manufacturing facility and is shipped to a client facility, when the component is received at a client's facility, it is often desirable for the client to independently verify that mark quality is sufficient for use with all of the readers at the facility and to decode the mark information to verify component type, to establish a record of received components, to begin a warranty period, etc. To this end, on one hand some known facilities include stationary verification systems akin to the verification stations at the component manufacturing facility described above that perform various verification processes including decoding to verify mark quality. To this end, known verification systems, like the known verification station described above, include some stationary mechanism (e.g., mechanical locking devices, sensors, etc.) for precisely aligning the mark on the component with a stationary ideal light source and a stationary camera so that the camera can generate an image of the mark and a processor can then glean mark verifying information from the mark.
On the other hand, other facilities employ hand held verifiers where a hand held mark reader is supplemented with verification hardware and software for performing verification processes.
Prior to using a verifier to verify mark quality the verifier has to be calibrated so that, when operated, optimal images are obtained for verification purposes. Known verifier calibration processes require that a verifier unit be linked to a computer (e.g., a personal computer (PC)) where the computer is used to manually set calibration target parameters (e.g., reflectance measurements, dimension measurement, etc.). After target parameters are manually set a calibration target is placed in the verifier field of view (FOV) and the PC is used to initiate a calibration operation in which a sequence of images of the calibration target are obtained using different verifier settings (e.g., exposure times). For each image, the verifier measures various characteristics of the image and compares those characteristics to the calibration target parameters. The image sequence continues with different verifier settings until the image characteristics match or are substantially similar to the target parameters after which the verifier settings or operating parameters are stored for use during subsequent verifier operations.
While verifiers can be calibrated using the known processes wherein the verifiers are linked to a computer (e.g., a PC), PC based calibration processes are burdensome as the calibration software has to be installed and set up on the PC prior to performing the calibration process and a PC has to be present to facilitate the process.